Switching Impulse Research Articles

Electric field and discharge voltage characteristics of UHV AC transmission line–tower air gaps

In high voltage transmission projects, the discharge voltage prediction of practical air gaps is a troublesome and long-awaited objective. For transmission line–tower air gaps, full-scale discharge tests can be expensive and prolonging. For the gap geometries in practical engineering, we cannot completely simulate all of them. In this paper, test samples taken for simulation are two types of actual gap geometries used in UHV transmission systems. The discharge path needed for a 250/2500μs 1000 kV switching impulse was found. For this, the two-dimensional finite element models of a UHV cup-type transmission line and a UHV compact type transmission line were established for electric field calculation. Then some features were extracted from the hypothetic discharge channel between the bundled conductor and the tower. Thus, various electric field features of the geometries are obtained. These values are verified by comparing it with the values obtained from the extensive literature survey. Discharge voltage characteristics of both geometries are also calculated and compared for different gap distances.

Pinning exponential cluster synchronization for fractional-order complex dynamical networks with switching topology and mode-dependent impulses

In this paper, we focus on the global exponential cluster synchronization of switched fractional-order complex dynamical networks (FCDNs) with switching topology and impulses, where the impulse effects are independent or dependent of switched modal. Compared with the literature, impulsive effects can occur not at the mode switched moment, but also at the instants without me AII) with the average dwell time (ADT) and the mode-dependent average impulsive interval (MDAII) with the mode-dependent average dwell time, by adopting multiple Lyapunov functional approach, the inequality analysis technique and pinning control strategy, the global exponential cluster synchronization conditions are achieved. Finally, the validity of theoretical results is verified by two simulation examples.

Particle movement pattern in a 1-φ GIB under abnormal conditions

Power system comprises of various over voltages which are transient in nature namely lightning and switching phenomenon under abnormal conditions which cause flashover in Gas Insulated Bus-duct (GIB) if not protected properly. So, there is a necessity for GIS to have withstanding capability of lightning and switching. Otherwise they may cause shut down of the system. In this work, 1050 kV Lightning Impulse and 750 kV Switching Impulse is superimposed on normal frequency voltage class of 100 kV, 132 kV and 145kV and are given to 1-ΦGIB for finding peak radial movement for Al and Cu particles. The movement patterns for both lightning and switching over voltages are compared. All the simulation results are shown in this paper.

Stochastic Stability of Impulsive Switched Systems With Constrained Switching and Impulses

This letter studies stochastic stability for impulsive switched systems with constrained switching and impulses. Here, “constrained” means that at each discrete-time instant, the switching and impulse are limited in a subset of all the modes. Constrained switching and impulses exist widely in many physical systems due to limitations on system structures and information transmission. Under constrained switching and impulses, we investigate stochastic stability of impulsive switched systems in three cases. For each case, stability conditions are derived using multiple Lyapunov functions and mode-dependent average dwell-time, and thus relax the conservatisms caused by common Lyapunov function and average dwell-time. Finally, two numerical examples are given to illustrate the obtained results.

Extended Use for the Frequency Response Analysis: Switching Impulse Voltage Based Preliminary Diagnosis of Potential Sources of Partial Discharges in Transformer

The Frequency Response Analysis approach (FRA) is useful in the fault diagnosis of transformers. However, its usefulness in diagnosing any potential sources of Partial Discharge (PD) in transformers has not been thoroughly investigated so far. In this work, the use of Impulse voltage-based FRA (IFRA) in diagnosing inter-turn shorts and potential sources of PD were investigated on a 315 kVA, 11 kV/433 V transformer. Inter-turn shorts and PD sources were emulated and the usefulness of IFRA in their diagnosis was investigated while using switching impulse voltage at different magnitude levels as the test signals. For emulating the inter-turn shorts and the PDs, special tappings were provided on one of the 11 kV windings through the low capacitance bushings. Low voltage impulse was successful in diagnosing the inter-turn shorts, but unsuccessful in identifying the sources of PDs. During the test condition, the test voltage was adjusted with the presence of artificially created PD sources. The frequency response of the transformer before and after the inception of PD was observed and analyzed in this article. The FRA results demonstrated that the switching impulse voltage based IFRA approach at moderate voltages could be useful in diagnosing the presence of the potential sources of PDs.

Explicit numerical approximation for an impulsive stochastic age-structured HIV infection model with Markovian switching

This paper considers an impulsive switching human immunodeficiency virus (HIV) infection model incorporating the mean-reverting Ornstein–Uhlenbeck process. The model involve the virus-to-cell infection and cell-to-cell transmission and has an explicit age-dependent structure. Due to the exact solution of this system cannot be expressed explicitly, it is necessary to give a suitable numerical method to discuss the numerical solution. In this paper, we apply the truncated Euler–Maruyama (EM) method to investigate the explicit numerical approximation for the impulsive stochastic age-structured HIV infection model with Markovian switching. We study the pth moment boundedness of the numerical solution, and the corresponding strong convergence of such algorithm. Numerical simulations are presented to demonstrate the validity of our findings.

Shock wave propagation in long laboratory sparks under negative switching impulses

A series of 1.27 m air gap discharge tests under negative switching impulses were carried out to characterize shock wave expansion behavior along leader channels. A high-speed Schlieren system was used to identify shock wave propagation characteristics near the high-voltage electrode. According to the Schlieren images, three distinct types of shock waves were recognized during the leader propagation and after the air gap breakdown: (1) spherical shock wave (SSW), (2) cylindrical shock wave (CSW), and (3) bow shock wave (BSW). To the best of our knowledge, it is the first time to recognize SSWs at the point where the space leader meets the main channel and BSWs along the leader branch after the main leader bridges the air gap. According to the proposed velocity calculation method, the propagation velocity of SSW and CSW was calculated as a function of the shock radius, as well as the shock wave head of BSW. Moreover, a transient magnetohydrodynamics model was developed to predict shock wave front propagation characteristics of both straight and bending channels after breakdown. The predicted shock wave propagation velocity and shock radius showed good agreement with Schlieren images.

Effect of shield placement for transient voltage mitigation due to switching surges in a 33/11 kV transformer windings.

This study presents an investigation on the effect of shield placement for mitigation of transient voltage in a 33/11 kV, 30 MVA transformer due to Standard Switching Impulse (SSI) and Oscillating Switching Impulse (OSI) surges. Generally, the winding and insulation in transformers could experience severe voltage stress due to the external impulses i.e. switching events. Hence, it is important to examine the voltage stress and identify the mitigation action i.e. shield placements in order to reduce the adverse effect to the transformer windings. First, the resistances, inductances, and capacitances (RLC) were calculated for disc type transformer in order to develop the winding RLC equivalent circuit. The SSI and OSI transient voltage waveforms were applied to the High Voltage (HV) winding whereby the transient voltages were simulated for each disc. The resulting voltage stresses were mitigated through different configurations of electrostatic shield placements. The resonant oscillations generated due to switching surges were analysed through initial voltage distribution. The analyses on the transient voltages of the transformer winding and standard error of the slope (SEb) reveal that the location of shield placement has a significant effect on the resonant switching voltages. The increment of the shield number in the windings does not guarantee optimize mitigation of the resonant switching transient voltages. It is found that the voltage stress along the windings is linear once a floating shield is placed between the HV and Low Voltage (LV) windings of the disc-type transformer under the SSI and OSI waveforms. These findings could assist the manufacturers with appropriate technical basis for mitigation of the transformer winding against the external transient switching overvoltage surges.

The failure arc paths of the novel device combining an arrester and an insulator under different pollution levels

Lightning strokes on transmission lines could trigger insulation failure if no protective measures are taken. Typically, a lightning arrester is used for this purpose. In order to combine the insulator and the lightning arrester as a single entity, a novel lightning protection composite insulator, combining an arrester and an insulator was developed for 10 kV distribution lines. Studied in this paper are the various arc paths of the novel insulator. The arc path tests under both AC and impulse voltage were conducted. The findings indicate that low, medium, high, very high, and extremely heavy pollutions caused different types of arcings under AC voltage. In addition, arc paths were affected by both the pollution level and the magnitude of impulse voltage. Based on the arc paths recorded by a high-speed camera, the flashover modes can be divided into three categories (flashover of the air gap, flashover of silicone rubber sheds in insulation section, and flashover of the whole insulator). More specifically, we defined and analyzed 14 types of arc paths in detail, and the critical pollution level (0.1 mg/cm2) of normal operation were obtained. Further, the statistical probability of each arc under impulse voltage was calculated. Due to the complexity of the arc paths under the switching impulse voltage, a 90% probability distribution figure of arc paths with different Us (switching impulse voltage) and ESDD (equivalent salt deposit density) was presented according to the test results. At last, we discuss the impulse voltage waveform corresponding to the typical arc path and describe the research prospect. The research results in this paper present the failure modes of the novel lightning protection insulator, and the results can be used for designing insulators for various pollution levels.

Study on Laminated Bus Bar for High-pulse Power Converter Module

Aiming at the problems of high switching overvoltage of power semiconductor devices and unbalanced current of parallel power devices in high-pulse power converters, this paper proposes a laminated bus bar of symmetrical path on the basis of the theoretical analysis and key points of laminated bus bar. The finite element simulation software was used to analyze the stray inductance of laminated bus bars. The actual stray inductance and overvoltage of the converter commutation circuit were measured by single pulse experiment. The results show that the laminated bus bar of symmetrical path can effectively reduce stray inductance, suppress switching impulse overvoltage and improve the current balance of the parallel power devices. It is of great significance to analyze the performance of laminated bus bar of symmetrical path, and it can be used for high-pulse power conversion technologies.

Stability and stabilization of impulsive switched system with inappropriate impulsive switching signals under asynchronous switching

The main objective of this paper is to study the stability and stabilization problems for a class of impulsive switched systems with inappropriate impulsive switching signals under asynchronous switching. Here, “inappropriate” means that the impulse jump moment may be inconsistent with the asynchronous switching moment or the system switching moment. And “asynchronous” implies that the switching of controller modes lags behind that of system modes. The hybrid case of stable or unstable subsystems combining with stable and unstable impulses is explored. A novel Lyapunov-like function is constructed, which is discontinuous at some special instants, including the switching instants, the instants when the system modes and filter modes are matched, and the impulse jump instants. Based on the novel multiple Lyapunov-like function, the sufficient conditions for the closed loop system to be globally uniformly exponentially stable (GUES) are obtained with admissible edge-dependent switching signals. Furthermore, by excogitating the state-feedback switching controller, the gain matrix of the controller can be obtained by solving the linear matrix inequalities. Finally, two numerical examples and simulation results are given to prove the effectiveness of our main results.

Unified Stability Criteria of Random Nonlinear Time-Varying Impulsive Switched Systems

This paper investigates the problem of noise-to-state practical stability in mean (NSpS-M) (which is a natural generalization of noise-to-state stability in mean) and the problem of almost sure global asymptotic stability (GAS a.s.) for a class of random nonlinear time-varying impulsive switched systems. By using the notions of average impulsive switched interval and Poisson process, unified sufficient stability criteria on NSpS-M and GAS a.s. are derived. Two remarkable distinctions from the existing results lie in that: (1) stabilizing, inactive and destabilizing impulses are simultaneously considered; (2) the coefficient of the derivative of a Lyapunov function is allowed to be a time-varying function which can be both positive and negative and may even be unbounded. As an accompaniment, a less conservative unified criterion on NSpS-M for a special case is also presented by taking into account the stabilization role of the gain constant of the time-varying coefficient. Two examples are provided to illustrate the effectiveness of our derived criteria.

Comments on “Finite-Time Control of Uncertain Fractional-Order Positive Impulsive Switched Systems with Mode-Dependent Average Dwell Time”

Some notes are presented on the paper “Finite-Time Control of Uncertain Fractional-Order Positive Impulsive Switched Systems with Mode-Dependent Average Dwell Time ” by Liu L. et al (Circuit Syst Signal Processing 37: 3739–3755, 2018). Fractional calculus has the memory property and this is relevant to the whole process from the initial value $$t_{0}$$ to the current time t. However, this important property is neglected in the above paper, and consequently, the main outcome is incorrect. A counter example is presented to verify our analysis.

Characteristics of AC PDs on epoxy insulation surface excited by different impulse voltages in SF6 gas

In this paper the behavior of partial discharges (PDs) on epoxy insulation under AC and impulse superimposed voltages are experimentally investigated in SF 6 gas. The lightning impulse (LI) and the switching impulse (SI) voltages with different polarity are superimposed on different phases of the AC voltage. PDs are measured by three sensors, a 50 Ω measurement impedance, an ultra-high frequency sensor and a photomultiplier tube. The max PD amplitude, PD pulse number and PD duration under AC voltage after an impulse voltage are summarized and analyzed. The effect of the impulse superposition phase, the impulse type and the impulse polarity on the characteristics of AC PDs are discussed. Results show that after a positive impulse voltage was applied on the positive semi-wave of AC voltage (0 to 180°), PDs in the negative half cycle of the AC voltage can be remarkably excited. A negative impulse voltage was applied on the negative semi-wave (180 to 360°), AC PDs can be initiated in the positive half cycle of AC voltage. PDs excited by a LI voltage is severe than excited by a SI. PDs excited by a positive impulse is intense than excited by a negative impulse.

De-noising of partial discharge signal using wavelet transform for GIS under HVDC

Abstract Detection and analysis of partial discharge (PD) have been regard as the most effective method for condition monitoring and asset management of gas-insulated structures (GIS) in the power system. However, PD detection sensitivity and accuracy are greatly influenced by on-site noise and interference, resulting in failures in PD severity assessment, defect identification or localization. Although de-noising of PD signal under AC was well studied, related investigations under DC have not been carried out. With the rapid development of HVDC technology, it is a new challenge to eliminate noise from PD signal under DC for diagnosis of related power facilities. Therefore, this paper dealt with the discrimination of PD signal based on wavelet transform (WT) techniques for HVDC GIS, aiming to improve the sensitivity and accuracy of insulation diagnosis. Experimental setup was configured to generate PD signal under DC and four types of artificial defects were fabricated to simulate typical insulation defects in GIS. The WT techniques were used to discriminate PD pulse sequences from background noise, amplitude modulation radio interference, non-sinusoidal noise, and switching impulse and the effectiveness was compared with a high-pass filter.

High-Frequency Impulse Modeling and Longitudinal Insulation Analysis of Bifilar Superconducting Coil

Bifilar coil is one of the most applicable structures used for resistive-type superconducting fault current limiter. However, the turn-to-turn (longitudinal) insulation of the bifilar coil under lightning and switching impulse is rather different from the conventional pancake coil. The longitudinal insulation is characterized as the distributed circuit of the coil under high-frequency excitation, and the capacitance, inductance, and resistance parameters are solved by finite element model. The influence of those resistance, inductance and capacitance (RLC) parameters on the accuracy of the model is analyzed, and two samples of one bifilar pancake coil and two series connected bifilar coils are fabricated for high-frequency impulse voltage testing. The experimental results are consistent with the simulation results. The initial voltage distribution and impulse response of two samples are calculated under standard lightning impulse. In the initial voltage distribution calculation, the interturn channels of one bifilar coil and two series-connected bifilar coils are subjected to a maximum voltage of 1 and 0.5 times the lightning impulse voltage.

Discharge of Air Gaps During Ground Potential Live-Line Work on Transmission Lines

Ground potential live-line work (GPLW) is a typical type of live-line work on transmission lines. In order to ensure the safety of live-line workers and reduce the consumption of test resources, the discharge of air gaps during GPLW on transmission lines was studied. Firstly, a breakdown voltage prediction method of GPLW air gaps was proposed, which can predict the breakdown voltage of GPLW air gaps. Subsequently, a discharge model of GPLW air gaps was proposed as well, so that the discharge characteristics of GPLW air gaps under different gap distances can be obtained more convenient. The prediction method and the discharge model were verified by switching impulse discharge tests of GPLW air gaps on UHV transmission lines, and the calculated results were close to the test results. Finally, the influence of live-line worker postures on discharge characteristics was studied. The results showed that workers should avoid causing protrusions of body parts in the course of work, which is more conducive to safety.

Computation of breakdown voltage of long rod-plane air gaps in large temperature and humidity range under positive standard switching impulse voltage

The 50% breakdown voltage of the air gap is an important basis for the design of the external insulation of the high voltage power systems, and the atmospheric conditions have a large impact on the breakdown voltage of the air gap. The temperature and humidity of the operating environment of the high voltage power systems have a wide range. The breakdown voltages of the gaps obtained in the laboratory are mostly near the standard atmospheric conditions, and there is no good way to calculate the discharge voltage outside the standard atmospheric conditions. This paper established a 50% positive switching impulse breakdown voltage prediction model based on the cuckoo search algorithm optimized support vector regression for the rod-plane air gap. This calculation model is used to predict the selected prediction data. The predicted results are basically consistent with the experimental results, and the effect is better than the atmospheric correction results. Finally, the method was used to calculate the 50% positive impulse breakdown voltage of the rod-plane air gap under the extreme temperature and humidity conditions in Beijing. This method provides a new idea for obtaining the air gap breakdown voltage under different atmospheric conditions.

Performance of Composite Outdoor Insulator Under Superimposed Direct and Switching Impulse Voltages

High Voltage Direct Current (HVDC) systems are increasingly being adopted around the world to integrate renewable resources, increase power transfer, and allow flexible grid operation. HVDC overhead lines play a critical role in this, and focus is needed on the research of composite outdoor insulators failure. In the case of a pole to ground fault of a bipolar scheme, the healthy pole experiences a slow transient overvoltage similar to a Switching Impulse (SI) superimposed on the operational DC voltage. However, there is no standard test for such voltage superimposition. This paper investigates the performance of a composite insulator stressed with such superimposition under dry and rain conditions. To determine the direct voltage influence on the flashover voltage, the results have been compared with the SI only case. Four different rain conductivities have been used in the test program because these insulators can be exposed to different acid conductive rain types, typical of industrialized environments. Both vertical and horizontal orientations have been studied. It was possible to conclude that, in most cases, the direct voltage pre-energization has a negative impact on the flashover performance. The increase in rain conductivity leads to lower flashover values, and the horizontal orientation outperforms the vertical configuration. Under these test conditions, the flashover voltages were all larger than a typical DC operational switching surge. Thus, in the case of pole to ground fault, the healthy pole failure risk appears to be low. However, further research is needed on higher voltages and polluted conditions.

Experimental Assessment on Air Clearance of Multiple Valve Unit Considering Switching Impulse and DC Superimposed Switching Impulse

Multiple valve unit (MVU), which converts AC to DC and DC to AC, is one of the key elements of high voltage DC (HVDC) transmission. Therefore, the insulation design of MVU against overvoltage should be considered for the stable and reliable operation of HVDC transmission system. Especially, the air clearance of MVU should be calculated based the switching impulse, since it is fatal to MVU in terms of electrical insulation. However, the previous studies were limited to wave front, and the air clearance of the switching impulse is specified only for an ultra-high voltage (UHV) above 750 kV. As a result, it is difficult to calculate the air clearance of MVU which must endure for a switching impulse under 750 kV. In addition, when the switching impulse introduced while the MVU is in normal operation, it is superimposed to DC and creates the most severe situation, but the studies on such subjects are also insufficient. Therefore, as a fundamental step to calculate the air clearance of MVU, the dielectric characteristics of switching impulse and DC superimposed switching impulse in air have been investigated. The experiments on switching impulse showed that the critical flashover voltage was varied according to the curvature of electrode in the gap distance, up to eight times of the electrode radius. However, beyond that gap distance, the critical flashover voltage became similar, regardless of the radius of electrodes. In case of the superimposed experiment, it was performed according to DC pre-stress level and the polarities of switching impulse. The results were most severe when the positive switching impulse was superimposed on the positive DC, and the peak voltage at which flashover occurs was independent of DC pre-stress.